Formation and dissolution of oxide film on zirconium alloys in 288°C pure water under γ-ray irradiation

Some thoughts on the mechanisms of in-reactor corrosion of zirconium alloys

“…Some supporting evidence for this has been obtained (Fig. 38) from specimens corroded in water under c-irradiation [107,150] and this has been supported by measurements of the dissolution of bulk stabilised zirconia specimens under similar conditions [107]. This could certainly provide a contributory mechanism for the enhanced uniform corrosion in BWRs seen on cladding with too small an initial SPP size, but does not explain nodular corrosion nucleation since no localised corrosion was observed in these experiments.…”

“…Oxide dissolution has also been proposed as a mechanism for enhanced corrosion in BWR water conditions [106], and evidence for reduced weight gains during gamma irradiation in 288°C water have been presented [107]. This has been matched by evidence for weight losses by bulk stabilised zirconia specimens exposed in similar conditions [29,68].…”

“…• No evidence has been produced for any direct effect of radiolytic radical species on a rate controlling process at the surface of ZrO 2 corrosion films. However, it has been proposed that the high peroxide concentration in BWR water acts by dissolving the ZrO 2 locally [107] (or possibly by dissolving SnO 2 or Fe 2 O 3 crystallites in the oxide grain boundaries). This hypothesis seems to be borne out by weight losses (or lower than expected weight gains) during corrosion of Zircaloy specimens and ZrO 2 ceramics during cirradiation in $300°C water [107].…”

“…However, it has been proposed that the high peroxide concentration in BWR water acts by dissolving the ZrO 2 locally [107] (or possibly by dissolving SnO 2 or Fe 2 O 3 crystallites in the oxide grain boundaries). This hypothesis seems to be borne out by weight losses (or lower than expected weight gains) during corrosion of Zircaloy specimens and ZrO 2 ceramics during cirradiation in $300°C water [107]. The effect of radiolytic species on the redox potentials of the various metal phases present is probably the most important factor here.…”

“…17. Model of dissolution process of zirconium oxide into water [107]. and without such progress there will continue to be difficulties in interpreting the in-reactor behaviour.…”